The present invention relates generally to a clamping connection assembly for retaining separable component portions of an assembled launch vehicle and more particularly to a device for controllably releasing at least a portion of the tension in a clamping connection prior to the separation of the separable component portions.
DISCUSSION
Connection assemblies, such as those that retain separable parts of an assembled launch vehicle provide important structural links in the primary load path of an assembled launch vehicle during both boost and ascent flight and, if necessary, during re-entry. For example, satellites frequently jettison a portion of their structure, such as a propulsion motor during their launch. As can be readily appreciated, spacecraft connection assemblies must be designed not only for low weight, but also for extremely high reliability due to the high cost of the spacecraft launch and the general inaccessibility to rectify any errors.
Designers in this field have recognized the desirability of using tension band clamping assemblies, to hold together separable components of an assembled launch vehicle, it is also desirable to reduce the shock produced during the release of the payload so as to reduce the risk of vibrating and damaging the payload of the assembled launch vehicle.
In the 1960s, a connection assembly design referred to as the Marman and was proposed which included a plurality of V-shaped retainers or shoe members that permitted the coupling of a pair of flanges positioned on the exterior surfaces of separable component parts of the assembled launch vehicle. A separable tension band was joined together by a pair of spaced pyrotechnic tension bolts that could adjustably vary the tension in the straps that held the V-shaped retainers together. The tension straps were utilized to create inwardly radial forces on the V-shaped retainers which in turn would clamp the flanges of the cylindrical housing structures together. This V-band coupling was configured to transfer loads and bending moments across the resulting structural joint of the connection assembly.
One problem noted with this approach concerns the shock that is produced upon the sudden release of tension in the clamp band. This tension is released from the clamp band when explosive bolts or bolt cutters are used. The magnitude of the shock delivered to the payload created by the sudden release of tension from the clamp band can exceed several thousand Gs and may be the greatest shock experienced during a launch. This problem is further aggravated by the trend towards larger and heavier payloads, since such payloads generally require the use of a clamp band that can produce higher levels of tension to properly secure the payload to the launch vehicle. As the shock produced upon the sudden release of tension from the clamp band varies with the level of tension in the clamp band, the use of a higher tension clamp band increases the risk that the sensitive spacecraft instrumentation will be damaged as a result of the sudden release of tension from the clamp band.
It is one object of the present invention to provide a tension-relieving apparatus to selectively release at least a portion of the tension in a structure.
It is a further object of the present invention to provide a tension-relieving apparatus that releases tension in a structure at a controlled rate.
It is yet another object of the present invention to provide a clamping apparatus having a tensionable band member whose tension may be controllably released to reduce the shock created when the band member is separated from a pair of separable spacecraft components.
In one form, the present invention provides a tension-relieving apparatus for reducing a level of tension in a structure. The tension-relieving apparatus includes a housing, a piston, a spacer member, and a heat source. The housing has a wall member that defines a piston cavity. A rod aperture is formed in a first end of the wall member. The piston assembly has a rod and a piston. The rod extends through the rod aperture. The piston is disposed in the piston cavity and is coupled to an end of the rod. The spacer member is disposed in the piston cavity. The spacer member is transformable between a first condition and a second condition, with the first condition maintaining the piston at a first distance from the end of the housing. The heat source is coupled to the housing, the piston assembly, and the spacer member and provides heat to selectively cause the spacer member to transform to the second condition wherein the spacer member transforms to its second condition to permit the rod to advance toward the first end of the housing. Advancement of the piston toward the first end of the housing relieves a predetermined portion of the tension in the structure.